1. Field of the Invention
The present invention generally relates to remote sensing of a tornado and, more specifically, to a system designed to receive acoustic emissions associated with a tornado, identify the emissions, and sound an alarm.
2. Description of Related Art
Tornados represent a significant hazard to persons living in many regions of the world. Advanced warning of an approaching tornado allows people to take shelter, thereby reducing the probability of injury or death.
The National Weather Service uses various radars in the U.S. to identify when conditions are conducive for the formation of a tornado and, based on identification of those conditions, issues tornado watches and warnings over the broadcast media. However, the time required to issue warnings and the resolution of the radar currently used by the National Weather Service limits the specificity of the warnings. For example, the alerted area often covers several hundred square miles, and the probability of a tornado affecting any particular location within a warned area is thus vanishingly small. As a result, tornado warnings and watches issued by the National Weather Service can at best serve to heighten the sensitivity of persons in the affected area to the signs, visual and aural, of an approaching tornado. For many individuals, despite the warnings and watches, the chance of reaching a shelter may already have passed by the time the tornado is actually observed.
The sounds of tornados have previously been described in literature and reported by the broadcast media in anecdotal form. While interviews with survivors of tornados suggests that the sound level generated by the tornados is very high and that the sound is distinctive, actual sound recordings of the tornados are often contaminated by voices and other background noise. Nevertheless, the anecdotes have been borne out by the inventors' analysis of the best recordings, which shows that tornados do in fact have similar acoustic spectra, even though the actual mechanism for sound production has not been specifically identified.
There are a number of devices available in the marketplace which warn of an approaching tornado, but none makes use of the tornado's acoustic emissions. The most widely used is a radio receiver tuned to the National Weather Service which sounds an alarm when the National Weather Service issues a severe weather warning although, as noted above, these warnings are general in nature and cover a large area.
Most other conventional tornado warning devices are based on the emission of electromagnetic radiation which is often associated with a severe storm. The electromagnetic radiation is received by some type of radio frequency receiver, and an alarm is sounded when the electromagnetic signal meets specified criteria. For example, U.S. Pat. No. 3,245,078 (Kohl) discloses a system for tracking the electromagnetic emissions of multiple weather patterns. This pattern includes a pulse counter for counting the number of times the electromagnetic signal received exceeds a proportion of its average peak value per unit time. U.S. Pat. No. 3,810,127 (Bacon) and U.S. Pat. No. 3,646,540 (Cooper) also disclose devices which detect the radio frequency emissions of an approaching tornado, while U.S. Pat. No. 2,928,277 (Cavanaugh) discloses a device which employs an active radar or sonar measurement. On the other hand, a completely different approach is disclosed by U.S. Pat. No. 4,632,052 (Green), which discloses a simple mechanical device to warn of sudden drops of barometric pressure that may indicate the approach of a tornado.
While many of the prior devices have the potential to save lives by warning of an approaching tornado, each has disadvantages which have prevented their widespread utilization in affected areas. Active radar or sonar systems are generally too complex and expensive for individual use, while the remaining systems suffer from a variety of problems, including the problem of false alarms.
The present invention, in contrast, for the first time effectively uses the fact that tornados emit sounds which are sufficiently unique to identify and use as a basis for sounding an alarm, and therefore may be detected by a relatively simple and inexpensive passive acoustic receiver. While passive acoustic devices have been previously used for detection purposes in a variety of unrelated contexts, such as for monitoring highway noise, detecting intruders, and the like, they have not been used for detecting tornadoes.